1. Field of the Invention
The invention relates to an information signal processing apparatus for processing an information signal.
2. Related Background Art
Hitherto, a CRT is generally used as a display apparatus of a video signal. The CRT has light emitting characteristics as shown in FIG. 1 for an input voltage. The light emitting characteristics can be expressed by the following equation when it is assumed that V indicates an input voltage, L, shows a radiation luminance, and k denotes a proportional constant. EQU L=kV.sup..gamma. (.gamma.=about 2.2) (1)
In a television system, therefore, a process called a gamma correction is executed as an information signal process in order to correct the light emitting characteristics at the time of photographing. The gamma correction can be expressed by the following equation when it is assumed that a luminance level is set to E and the level after completion of the gamma correction is set to V. EQU V=E.sup.1/.gamma. ( 2)
FIG. 2 shows the gamma correcting characteristics by the above equation (2).
FIG. 3 shows a gamma correction circuit which is used in a conventional video camera or the like to perform the gamma correction mentioned above. In the diagram, reference numeral 1 denotes an input terminal to which an input signal (negative polarity) is supplied; 2 a transistor for converting an impedance; 3 an emitter resistor to decide an emitter current of the transistor 2; 4.sub.1 to 4.sub.n diodes; 5 and 6.sub.1 to 6.sub.n dividing resistors each for deciding an amplitude voltage of an output signal; E.sub.1 to E.sub.n power source voltages each for setting a polygonal point of input/output characteristics; and 7 an output terminal.
The operation of the gamma correction circuit shown in FIG. 3 will now be described. For example, when an input signal as shown in FIG. 4 is supplied to the input terminal 1, the input signal is output from the output terminal 7 through the impedance converting transistor 2 and the dividing resistor 5 connected to an emitter thereof. In this instance, when the potential of the output terminal 7 is further reduced than the potential which is lower than each of the polygonal point set voltages E.sub.1 to E.sub.n of the input/output characteristics by only V.sub.D (voltage.congruent.0.6 V! that is applied to the diodes 4.sub.1 to 4.sub.n), the diodes 4.sub.1 to 4.sub.n are made conductive. An output voltage of the emitter is divided by the dividing resistors: 5 and 6.sub.1 to 6.sub.n.
In this case, in the case where there is one combination of the diodes 4.sub.1 to 4.sub.n, resistors 6.sub.1 to 6.sub.n, and voltages E.sub.1 to E.sub.n, the input/output characteristics of the circuit are set to polygonal characteristics in which the number of polygonal points by the voltage division is equal to 1. When there are (n) such combinations, the polygonal characteristics having n polygonal points are obtained.
FIG. 5 shows the input/output characteristics when there are three polygonal points. Gamma correcting characteristics which are close to those shown in FIG. 2 and by equation (2) are obtained. In FIG. 5, an input signal and an output signal are shown by relative values.
Therefore, to raise a precision of the gamma correction, it is necessary to increase the number of polygonal points by increasing the number of diodes 4.sub.1 to 4.sub.n, the number of dividing resistors 6.sub.1 to 6.sub.n, and the number of polygonal point setting voltages E.sub.1 to E.sub.n.
In the television system, an outline correcting apparatus is used as an information signal processing apparatus in order to emphasize an outline of a display image. FIG. 6 shows a conventional outline correcting apparatus.
In FIG. 6, reference numeral 31 denotes an input terminal of a video signal; 32 a delay circuit to match the phases of the video signal and outline signal; 34 an outline signal extraction circuit to extract the outline signal from the video signal which was input from the input terminal 31; 36 a gain adjustment circuit to adjust an amount of outline which is applied to the video signal by adjusting a gain of the outline signal; 37 an adder to add the outline signal to the video signal; and 38 an output terminal of the outline corrected video signal.
The operation of the outline correcting apparatus shown in FIG. 6 will now be described.
When a video signal as shown in FIG. 7A is supplied to the input terminal 31, an outline signal as shown in FIG. 7B is extracted by the outline signal extraction circuit 34. The outline signal is adjusted to a proper level by the gain adjustment circuit 36 and, after that, it is added to the original video signal by the adder 37. For example, as shown in FIG. 7C, the addition output has a waveform whose outline is emphasized by an overshoot portion and an undershoot portion. Such a waveform signal is output from the output terminal 38.
Since the conventional gamma correction circuit is constructed as shown in FIG. 3, there are the following problems.
(1) An overall blank state of the picture plane cannot be automatically adjusted and cannot be remote controlled from the outside.
(2) The input/output characteristics of the gamma correction cannot be remote controlled from the outside.
(3) To perform the gamma correction at a high precision, a larger number of diodes 4.sub.1 to 4.sub.n need to be used, so that a junction capacitance of the diodes becomes a load of the circuit and frequency characteristics are deteriorated by the AC and DC levels of the input signal.
On the other hand, since the conventional outline correcting apparatus is constructed as shown in FIG. 6, no problem occurs in case of executing the gamma correction after the outline was corrected. However, in case of performing the outline correction after completion of the gamma correction, there are the following problems.
The outline correction is obtained b)y adding the overshoot portion and undershoot portion each having the same amplitude to the edge portion of the image as shown in FIG. 7C. However, in case of outputting such a signal onto the CRT and displaying, the amplitudes of the undershoot portion and overshoot portion remarkably differ as shown in FIG. 8 due to the light emitting characteristics of the CRT as shown in FIG. 1. Particularly, the undershoot portion decreases. Thus, there is an impression such that the image is floating up and the image in which the natural feeling and stereoscopic feeling are insufficient is obtained.
As an information signal processing apparatus, in the case where data which was input to the input port is transferred to a memory and the data in the memory is selectively transmitted to a plurality of output ports, hitherto, such transmitting operations are controlled by using both of a method of transmitting the data to the input and output ports in accordance with the fixed order of priority and a method of transmitting the data from the input and output ports in accordance with the order of transmission requests.
According to the above conventional data transmitting method mentioned above, in the case where the transmission requests are frequently generated or are continuously generated, a problem such that each input and output ports are selected is not constant, so that a port in which an accumulation amount of data is large and a port in which a data accumulation amount is small occur. Therefore, in case of using such a method to an apparatus of a large information amount such as an image recording apparatus or the like, it is necessary to prepare an FIFO (First-in, First-out) memory or the like of a large capacity in the input and output ports.